There has been proposed an optical disc for recording or reproducing predetermined information signals, such as audio or video signals. The optical disc is constituted by a disc base plate formed of, for example, polycarbonate or acrylic resin and on which pits and grooves are formed, and a metal material, such as aluminum, deposited thereon as a reflective film.
Among the techniques of depositing the metal material on the disc base plate, an evaporation method, an ion plating method, and a sputtering method are known.
The evaporation method consists in heating a metal material, acting as an evaporation source, in a vacuum chamber for evaporating the metal and depositing the metal material on the disc base plate placed in the so-produced metal vapor. Since the processing cannot be started with this method until the metal material is vaporized sufficiently, a so-called batch system is employed for increasing the quantity of the optical discs produced for a unit time, according to which plural optical discs are produced by one evaporating operation of the metal material with the use of a large-sized vacuum chamber capable of accommodating plural optical discs. Thus the apparatus is complicated in structure and increased in size so that restrictions are imposed on the floor space. In addition, since continuous operation cannot be performed, it is difficult to shorten the processing time to increase the production efficiency significantly.
Similarly to the evaporation method, the ion plating method consists in vaporizing and ionizing the metal material in a vacuum chamber containing a gas for electrical discharge, such as argon, under a reduced pressure, and applying an electrical field thereto for accelerating the ionized gas and the ionized metal vapor toward the disc base plate for depositing the metal material on the disc base plate. With this ion plating method, similarly to the above described evaporation method, the metal vaporizing operation is time-consuming, so that the batch system needs to be employed for increasing the production quantity of the optical discs per unit time. Hence, it is difficult to reduce the size of the processing apparatus or to shorten the processing time.
The sputtering method has advantages that the processing can be completed in a short time, a continuous processing is possible, and the films can be formed on the optical discs under the same conditions, so that the method is suited to mass production or to production of a number of different types of the disc base plates.
The sputtering method consists in sealing a gas for electrical discharge, such as argon, under a reduced pressure, in a vacuum chamber containing a disc base plate and a metal material, such as aluminum acting as a target, and applying an electrical field to said vacuum chamber for ionizing the gas. The thus-ionized gas bombards the metal material, thereby ejecting atoms or molecules of the metal material, so as to be deposited as a thin film on the disc base plate.
Among the known apparatus for performing the sputtering operation is a so-called load-lock type sputtering apparatus shown for example in FIG. 26. This sputtering apparatus includes a vacuum vessel 10i and a sputtering station 102 provided above the middle portion of the vacuum vessel 101. An inlet 101a by means of which a disc base plate 103 is introduced into the vessel 101 and an outlet 101b by means of which the disc base plate 103 is transported out of the vessel 101 are provided at the opposite sides of the vessel 101.
This sputtering apparatus also includes a transport device 104 for transporting disc base plates. The transport apparatus 104 is adapted for transporting the disc base plates 103 from outside of the vacuum vessel 101 into the vacuum vessel 101 by means of the inlet 101a and transporting the disc base plates 103 out of the vacuum vessel 101 by way of the sputtering station 102 and the outlet 101b.
A plurality of opening/closure valves 105 are provided within the vacuum vessel 101. These opening/closure valves 105 are adapted for subdividing the inside of the vacuum vessel 101 into a plurality of hermetically sealed cells or chambers along the transport direction of the disc base plates 103. These opening/closure valves 105 are adapted for maintaining the portions of the vacuum vessel 101 associated with the sputtering station 102 in a high vacuum state and are opened or closed with the progress in the transport operation of the disc base plate 103. In this manner, the chambers of the vacuum vessel 101 are maintained at a predetermined pressure. That is, the portions of the vacuum vessel 101 adjacent to the inlet 101a and the outlet 101b are at a lower vacuum, while the middle sputtering station 102 is at the highest vacuum.
Within the sputtering station 102, a target made of a metallic material 106 to be applied to the disc base plate s arranged, and a gas for electrical discharging is present therein under a high vacuum state. An electrical field application apparatus, not shown, for applying an electrical field, is provided in the sputtering station 102.
With the above sputtering apparatus, the disc base plate 103 is transported from the inlet 101a into the inside of the vacuum vessel 101 as far as the position of the sputtering station 102 maintained at the highest vacuum. The above mentioned sputtering operation is performed at this position so that a thin metal film is deposited on the disc base plate 103. This sputtering operation is completed within, for example, two to three seconds. The optical disc, on which the thin film has been formed, is transported to the portions of the vessel 101 maintained at progressively lower vacuums and discharged out of the vacuum vessel 101 by way of the outlet 101b.
Among the apparatus so far known for performing the sputtering operation on the disc base plates 103 is a apparatus shown in FIGS. 27 and 28. The sputtering apparatus shown in FIGS. 27 and 28 is provided with a transport table 108 which is rotatably supported in a cylindrical vacuum chamber 107 by a supporting shaft 108a and on which are supported a plurality of disc base plates 103. A circular disc inlet/outlet 107a having a diameter slightly larger than the outside diameter of the disc base plate 103 is provided above the upper surface of the vacuum vessel 107, while there is also provided a sputtering station 102, similar to the above described sputtering apparatus, at a position substantially facing the disc inlet/outlet 107a.
The transport table 108 is rotated in a direction shown by an arrow r in FIGS. 27 and 28 about the supporting shaft 108a as the center of rotation, whereby the disc base plate 103 introduced into the vacuum chamber 107 by way of the disc inlet/outlet 107a is transported to a position facing the sputtering station 102. The transport table 108 is transiently kept at a standstill at the position facing the sputtering station 102. While the transport table is at a standstill, the sputtering operation is performed on the disc base plate 103. After the end of the sputtering operation, the transport table 108 is again rotated in a controlled manner for transporting the disc base plate 103 to the position facing the disc inlet/outlet 107a.
The disc base plate 103 is placed on a disc supporting table 108b fitted into a recess formed on the transport table 108. A lid 111 for maintaining the vacuum chamber 107 in a vacuum is provided at the disc inlet/outlet 107a.
With the above described sputtering apparatus, the disc inlet/outlet 107a is kept closed by at least one of the disc supporting table 108b or the lid 111 by the operation of thrust shafts 109, 110 projecting from the bottom surface into the interior of the vacuum chamber 107. In this manner, the disc base plate 103 may be transported into and out of the vacuum chamber 107 under a state in which atmospheric air is prevented from intruding into the inside of the vacuum chamber 107.
It is noted that, with the sputtering apparatus shown in FIG. 26, even if the time necessary for the sputtering operation itself could be reduced, the time necessary for the sputtering operation itself could be reduced, the time necessary for the transport operation of the disc base plate 103 into and out of the sputtering apparatus is s long that it is difficult to reduce the residence time in the apparatus. On the other hand, if the residence time is long as compared with the sputtering time, a large number of disc base plates are caused to dwell in the apparatus thus increasing the size of the apparatus and the floor area. In addition, since the vacuum vessel 101 is increased in space, a larger exhaust pump needs to be used in order to maintain a sufficiently low vacuum in the vacuum vessel to guarantee satisfactory sputtering, with the result that the apparatus is necessarily increased in size.
Besides, in the above-described sputtering apparatus, since a plurality of opening/closure valves are used for maintaining the state of vacuum within the vacuum vessel, the apparatus is complicated in structure and hence becomes more difficult to produce, while the maintenance of the apparatus becomes more troublesome due to lowered durability of valves or the like devices. For example, the above mentioned opening/closure valves need to be replaced after 100,000 repetitions of the opening/closing operations.
The sputtering apparatus shown in FIGS. 27 and 28 is also inconvenient in that, similarly to the sputtering apparatus shown in FIG. 26, the time necessary in transporting the disc into and out of the apparatus cannot be reduced without considerable difficulties and the apparatus cannot be reduced in size, while the production costs of the apparatus cannot be lowered.
The present invention has been proposed in view of the above described status of the art, and is aimed at providing a sputtering apparatus which is small in size, simplified in structure, easy in production and maintenance and excellent in production efficiency and with which the production quantity per unit time can be expected to be increased significantly.
The present invention also aims at providing a processing system in which equipment common to the sputtering apparatus, such as a sputtering power source unit, can be used to reduce the costs of the apparatus, and in which the production quantity per unit time can be expected to be increased significantly to increase production efficiency.